Low-dose human chorionic gonadotrophin (HCG) combined with a severe diet remains a popular treatment for obesity, despite equivocal evidence of its effectiveness. In a double-blind, placebo-controlled study, the effects of HCG on weight loss were compared with placebo injections. Forty obese women (body mass index > 30 kg/m2) were placed on the same diet supplying 5000 kJ per day and received daily intramuscular injections of saline or HCG, 6 days a week for 6 weeks. A psychological profile, hunger level, body circumferences, a fasting blood sample and food records were obtained at the start and end of the study, while body weight was measured weekly. Subjects receiving HCG injections showed no advantages over those on placebo in respect of any of the variables recorded. Furthermore, weight loss on our diet was similar to that on severely restricted intake. We conclude that there is no rationale for the use of HCG injections in the treatment of obesity.